Synthetic polyamides stabilized with thermally stable ionic tin salts



United States Patent Ofifice 3,067,168 Patented Dec. 4, 1962 1 3,067,168 SYNTHETIC POLYAMIDES STABILIZED WITH TI-IERMALLY STABLE IONIC TIN SALTS William A. B. Pin-don, Waynesboro, Va., assignor to E. L

du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware No Drawing. Filed May 13, 1960, Ser. No. 28,822

6 Claims. (Cl. 260-45.75)

This invention relates to the preparation of stabilized synthetic fiber-forming polyamides by the addition of a tin salt.

It is known that certain inorganic salts, such as CuCl stabilize polyamides against the action of heat. However, it is also known that polyamide yarns and fabrics containing these prior art stabilizers suffer from discoloration and severe degradation upon bleaching.

The most important object of this invention is to provide a non-discoloring stabilizer for polyamides.

Another important object of the invention is to provide a heat and light stabilized polyamide yarn which also shows improved retention of tenacity when bleached.

In accordance with the present invention, a heat and light stabilized polyamide yarn is prepared by incorporating a tin salt in the polyamide. The tin salt may be any thermally stable ionic stannous or stannic compound which is soluble in polyamides. Suitable salts include stannic and stannous chloride, bromide, sulfate, phosphate, acetate, butyrate, laurate, palmitate, stearate, adipate, pimelate, subearate, azelate, sebacate, phthalate, isophthalate, and terephthalate.

The tin salt may be added in trace amounts to the polyamide-forming reactants prior to or during polymerization or to the polyamide itself in the molten state. The salt may also be applied by swelling the polyamide yarn in an aqueous salt solution and drying the swollen yarn to remove the water, leaving the salt in the yarn.

The concentration of the tin salt in the polymer may be between about 0.001 and 1.0 mol percent (based on the repeat unit of the polymer) and preferably is between 0.01 and 0.10%.

EXAMPLE I A stainless steel autoclave was purged of air, filled with nitrogen and charged with an aqueous solution containing 49% by weight of hexamethylene diammonium adipate, 0.39% by weight of acetic acid, and 0.01 mol percent (based on the repeat unit of the polymer) of stannic chloride in the form of an aqueous solution containing by weight of the chloride. The autoclave was heated to a temperature of 240 C. at 250 psi. pressure. At this stage, bleeding off of water vapor was commenced. The polymerization cycle was continued as in Example I of US. Pat. No. 2,163,636. Upon completion of the polymerization reaction, the molten polymer having a relative viscosity of 40 was extruded in the form of a ribbon on a. casting wheel. After quenching, it was cut into chips suitable for remelting at the grid of a spinning assembly. The polyhexamethylene adipamide flake, containing 0.01% by weight of stannic chloride, was melted in a steam atmosphere in the manner disclosed by Waltz in US. Pat. No. 2,571,975, spun at a rate of 517 yards per minute and drawn into a 70 total denier l3 filament yarn.

The heat stability of the yarn was measured by exposing the yarn in an oven at 180 C. for five hours and measuring the break tenacity before and after exposure. From these measurements, the percentage break tenacity retained was calculated, a high percentage break tenacity retained after heating indicating a good heat stability. The results are recorded in Table I in an after heating column and compared to a control yarn (control I) prepared following the same technique but not containing the stannic chloride. The results are also compared to a yarn (control II) prepared following the same technique but containing the prior art stabilizer CuCl instead of SnCl The relatively low percentage break tenacity retained by this yarn (control II) after bleaching is indicative of the extent of degradation.

Another sample of the yarn was bleached in a solution of 0.125% peracetic acid and 0.01% Calgon (adjusted to a pH of 6.5) at F. for 15 minutes, and then rinsed in distilled water. Calgon is a sodium phosphate compound which h'as utility as a water softener. Its percentage break tenacity retained after bleaching was measured, the results being summarized in Table I in an after bleaching column.

Again another sample of the yarn was tested for 400 hours in a Weatherometer as described in US. Pat. No. 2,887,462. Its percentage break tenacity retained after light exposure was measured. The results are summarized in Table I in an after light exposure column.

Table I clearly shows the superior combination of heat, light, and bleach stability of yarns containing the stabilizer of this invention.

EXAMPLE II EXAMPLE III Polyhexamethylene adipamide was prepared, spun into yarn and tested following the general techniques of EX- ample I but, instead of 0.01 mol percent stannic chloride, 0.01 mol percent (based on the repeat unit of the polymer) of stannic phosphate was used. The improvements are shown in Table I.

EXAMPLE IV Polycaproamide is prepared and 0.01 mol percent stannic adipate is added to the monomer (caprolactam) prior to the polymerization. Improvements in break tenacity retained upon bleaching or heating or upon light exposure are similar to those found in Example 11.

TABLE I Percent Break Tenacity Retained After Heating Alter Light Exposure Control I--- Control 11.. Example I-. Example II- Example III It is apparent that the tin salts may be used in combination with other additives which improve the end product, such as potassium iodide, and that tin salts equivalent to those which have been exemplified may be used without departing from the spirit of the present invention which is otherwise intended to be limited only by the scope of the appended claims.

I claim:

1. A composition of matter comprising a synthetic linear polyamide taken from the group consisting of polyhexamethylene adipamide and polycaproamide, said polyamide containing a trace of a thermally stable ionic tin salt in an amount not exceeding 0.10 mol percent (based on the repeat unit of the polyamide) 2. The composition of claim 1 wherein the tin salt is a selected from the group consisting of stannic chloride, stannic adipate and stannic phosphate.

3. A shaped article consisting essentially of a synthetic linear polyamide taken from the group consisting of polyhexamethylene adipamide and polycaproamide, said polyamide containing a trace of a thermally stable ionic tin salt in an amount not exceeding 0.10 mol percent (based on the repeat unit of the polyamide).

4. The shaped article of claim 3 wherein the tin salt is selected from the group consisting of stannic chloride, stannic adipate and stannic phosphate.

5. A spinning solution consisting essentially of molten polyhexamethylene adipamide having a trace of a thermaliy stable ionic soluble tin salt selected from the group consisting of stannic chloride, stannic adipate and stannic phosphate in solution therewith in an amount not exceeding 0.10 mol percent (based on the repeat unit of the polyamide).

6. A spinning solution consisting essentially of a molten polyamide selected from the group consisting of polyhexamethylene adipamide and polycaproamide, said molten polyamide containing about 0.01 mol percent (based on the repeat unit of the polyamide) of a stabilizer in solution therewith, said stabilizer being selected from the group consisting of stannic chloride, stannic adipate and stannic phosphate.

References Cited in the file of this patent UNITED STATES PATENTS 2,514,221 Albert July 4, 1950 2,715,111 Weinberg Aug. 9, 1955 2,929,801 Keller Mar. 22, 1960 FOREIGN PATENTS 1,051,521 France Jan. 18, 1954 81,485 Netherlands May 15, 1956 

1. A COMPOSITION OF MATTER COMPRISING A SYNTHETIC LINEAR POLYAMIDE TAKEN FROM THE GROUP CONSISTING OF POLYHEZAMETHYLENE ADIPAMIDE AND POLYCAPROAMIDE, SAID POLYAMIDE CONTAINING A TRACE OF THERMALLY STABLE IONIC TIN SALT IN A AMOUNT NOT EXCEEDING 0.10 MOL PERCENT (BASED ON THE REPEAT UNIT OF THE POLYAMIDE). 